The honest answer, with numbers from the studies that measured it, plus a seven day protocol to find yours instead of trusting a marketing page.
The honest answer is that nobody can tell you, and any page that gives you a flat number invented it. The most rigorous study I could find is more extreme than any app blocker: it cut participants from 314 minutes of daily phone use to 161, roughly two and a half hours a day, by blocking mobile internet entirely for two weeks. It also found that only a quarter of the people who signed up actually managed to comply, and that use climbed back to 265 minutes two weeks after the block came off. That is the real shape of the answer: a large drop, an ugly compliance rate, and a rebound. Your own number is the only one worth anything, and it takes seven days to get it.
What the best study actually measured
The study is Blocking mobile internet on smartphones improves sustained attention, mental health, and subjective well-being, published in PNAS Nexus. 467 people enrolled, 313 completed all three surveys. Participants installed an app that blocked all mobile internet, Wi-Fi and mobile data both, while leaving calls and texts working.
The numbers, for the intervention group:
| Measure | Before | After 2 weeks | 2 weeks later |
|---|---|---|---|
| Daily screen time | 314 min | 161 min | 265 min |
The delayed group, which acted as the control first, went from 336 to 322 minutes while unblocked, then dropped to 190 once their turn came. The pattern replicates. So does the rebound.
Two caveats, and they matter more than the headline.
First, this is not an app blocker. This is the whole internet gone from the phone for two weeks. An app blocker that removes Instagram, TikTok and YouTube is a fraction of that intervention, so expect a fraction of that effect.
Second, compliance. 119 people, 25.5% of those who committed, met the study’s preregistered definition of compliant. Three quarters of volunteers who signed up for a research study, knowing they were being measured, could not keep the block on. If you are wondering whether you will stick to it, that is the number to sit with, not the 153 minutes.
What the study does support, on the pooled sample: 90.7% of participants improved on at least one of attention, mental health or well-being. Sustained attention improved by an effect size the authors describe as about the same magnitude as ten years of age related decline, running the other way. That is a genuine result and a modest one.
You cannot estimate this from memory
Before you measure anything, throw out your guess.
A meta-analysis in Nature Human Behaviour, covering 106 effect sizes, compared what people said about their media use with what their devices logged. Self-reported use correlates only moderately with logged measurements, and the authors conclude that self-reports were rarely an accurate reflection of actual use. Measures of problematic use, the “I’m on my phone too much” kind of question, matched the logs even worse.
So “I probably spend an hour on Instagram” is not data. Neither is “I’ve cut way down since I installed this.” Both are the same instrument, and the instrument is broken.
The only screen time number worth trusting is one you measured twice, on yourself.
This is also why I do not put a claim on Lock’s homepage about hours saved. I have no way to compute it for you, and the number I would compute for myself would be a sample of one.
Saved time is not gained time
An hour taken off Instagram does not become an hour of work. It has to go somewhere, and where it goes is the part most articles skip.
The PNAS Nexus study tracked this. When mobile internet was blocked, participants reported more time in what the authors call the offline world: socializing in person, exercising, being in nature, hobbies, reading. That was the largest time use shift they measured. Sleep went up slightly. Digital communication, texts and calls, did not change. Self control scores improved.
Notice what is absent from that list: work output. Nobody measured whether these people got more done, and I would not assume it. My own experience is that a locked phone moves the leak to the laptop unless I do something about the laptop too. I wrote about that limit in why willpower isn’t a feature, and it has not changed.
If you are buying an app blocker to ship more code, be aware you are buying evidence for calmer evenings, not for higher output.
Measure your own week
Here is the protocol. It costs nothing and it takes fourteen days.
Days 1 to 7, baseline, change nothing. Do not install a blocker. Do not try to behave. Open Digital Wellbeing on day 8 and write down two things: total daily average, and the daily average for the two or three apps you actually want to cut. Per app matters, because the total is polluted by maps, music and calls.
Days 8 to 14, blocker on. Same apps, same routine, same working days. Weekends distort the average badly, so compare like for like or run both weeks Monday to Sunday.
Day 15, compare. Two numbers, before and after, for the specific apps. That difference is your answer. It is the only one that applies to you.
Two things to record alongside the numbers, because they explain the numbers:
- How many times you unblocked. In Lock this is visible in the stats screen, which counts sessions, total locked time, average session length and a week over week comparison. Lock deliberately does not track your screen time, that is Digital Wellbeing’s job, so you will be reading two screens. Locked hours and screen time are different quantities and it is worth keeping them separate in your head.
- Whether you kept it on. A blocker you uninstalled on Thursday saved you nothing, whatever week one showed.
That second point has research behind it too. A University of Michigan field study of 42 people over five weeks compared a friction based tool, which makes the phone subtly annoying past a daily limit, against a conventional hard lockout. The friction tool reduced screen time about 16% more, and 62% of participants kept it active daily against 36% for the lockout. The gentler tool won on total time saved because people kept using it.
That is the trade I think about constantly with Lock. A physical tag is real friction, not a suggestion, but the tag is also why the app survives contact with a normal week: you are never locked out, you are just made to stand up. The emergency unlocks and the session timeout on the support page exist for the same reason. A tool that traps you gets uninstalled, and an uninstalled tool has an effect size of zero.
What to do this week
- Open Digital Wellbeing tonight and screenshot it. Not the weekly total, the per app breakdown. You need a before, and you cannot make one retroactively.
- Do nothing for seven days. The urge to fix it immediately is exactly what ruins the baseline.
- Then block the two or three apps that dominate the list. Two or three, not twelve. A block you resent is a block you undo. The setup guide covers where to put the tag, which matters more than which apps you pick.
- Compare on day fifteen, then again on day thirty. The second comparison is the honest one. The rebound in the study happened at exactly that distance, and it will tell you whether you built a habit or ran an experiment.
- Write the number down somewhere. If it is twenty minutes, that is twenty minutes. Small and true beats large and imagined.
I would rather you finish this article with a method than with a statistic. The studies are worth reading, and none of them are about you. Two weeks of your own logs are.